Errors Introduced by Multiphase Flow Correlations on Production Analysis Conference Paper uri icon

abstract

  • Abstract First and foremost, production analysis techniques require accurate rate and bottomhole pressure histories. In most cases the pressure history of the well is not measured directly at the bottomhole condition, but is calculated from surface measurements by the use of single or multiphase flow correlations. In some cases significant error is introduced through the use of these correlations. This paper evaluates the magnitude of such errors for oil and gas producers with regard to the estimation of flow capacity, completion efficiency, and effective drainage area. Synthetic cases are used as control sets in order to evaluate the sensitivity of the results to the various multiphase flow correlations and flowing conditions. In addition to synthetic (simulated) performance behavior, field cases are presented and the variance in estimated reservoir and completion properties is evaluated. The technical contributions of this paper are:Systematic evaluation of the effect of errors in flow rates and bottomhole flowing pressures on production data analysis --- using both synthetic and field derived well performance data.Qualitative guidelines as the effect of errors in rate and pressure on estimated reservoir properties.Establishment of the most relevant pressure drop correlations for use in practice. Introduction Production analysis techniques can be used to provide an understanding of the flow capacity of a well, the completion efficiency of a well, and the effective drainage area (or volume). As a methodology, these techniques treat the long term production of a well as an extended constant rate drawdown test in order to interpret the well performance and to estimate the reservoir and well parameters. The well established analysis/interpretation techniques require both accurate production rates and flowing bottomhole pressures. In most cases the flowing bottomhole pressure is not measured directly, but is calculated based on the measured (surface) tubing pressure profile and flow rate data. Pressure drop correlations for multiphase flow are used to "convert" the surface pressure profile into a bottomhole pressure profile suitable for analysis and interpretation. Depending on the (multiphase flow) pressure calculation method that is selected, as well as the producing conditions, significant errors in the calculated flowing bottomhole pressure can (and will) result --- which affects the estimation of reservoir/well parameters. Three synthetic (simulation) cases were constructed for the purpose of serving as control data sets for this study. Each case represents a single well reservoir producing from the center of a radial flow geometry system. These simple scenarios are used to avoid any multiwell (interference) effects, as well as partial or irregular boundaries, etc. Specifically, the cases considered for this study include:Fracture stimulated well, low permeability gas reservoir,Unfractured well, low permeability oil reservoir, andUnfractured well, high permeability oil reservoir. An appropriate multiphase correlation for each case was selected to control the simulator. The actual rates and bottomhole pressures were used to validate the production analysis techniques. New bottomhole pressures were then calculated utilizing different multiphase flow correlations, and the evaluation process was repeated. The results of each analysis were compared to the parameters used in the simulator in order to establish the conclusions in this paper. As a comprehensive statement, the results of this work highlight the need for to acquire flowing gradients periodically to calibrate the multiphase flow correlation. Background Theory The use of well production data to characterize reservoir performance has been utilized by the oil industry for many years. Early application of this technology is based on the empirical equations presented by Arps1 for rate-time decline curve analysis (semi-log rate-time plots). Decline curve analysis used the historical rate-time data of a given well to predict the future performance of that well.

name of conference

  • SPE Annual Technical Conference and Exhibition

published proceedings

  • All Days

author list (cited authors)

  • Cox, S. A., Sutton, R. P., & Blasingame, T. A

complete list of authors

  • Cox, Stuart Alan||Sutton, Robert P||Blasingame, Thomas Alwin

publication date

  • January 1, 2006 11:11 AM

publisher

  • SPE  Publisher